1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to a plasma display panel having bus electrodes of different respective structures on a display area and a non-display area.
2. Description of the Related Art
A Plasma Display Panel (PDP) is a flat display device that displays letters or graphics using light emitted by plasma generated in a gas discharge process. The PDP can be either a Direct Current (DC) PDP, in which an electrode for applying voltages from the outside is directly exposed to the plasma and a conduction current flows directly through the electrode, or an Alternating Current (AC) PDP, in which an electrode is covered by a dielectric and is not directly exposed to the plasma and a displacement current flows therethrough.
In a PDP, a sustain electrode is formed on a front substrate and the sustain electrode is covered by a front dielectric layer. A protective layer is formed on the front dielectric layer.
An address electrode is formed on a rear substrate that is disposed to face the front substrate and a rear dielectric layer is formed on the address electrode. A barrier rib that defines the discharge space is formed on the rear dielectric layer and a phosphor layer of red, green, and blue colors formed on an upper surface of the rear dielectric layer and an inner surface of the barrier rib.
On the other hand, an inner space between the front and rear substrates is a discharge space, into which an inert gas is injected.
Alternatively, a PDP includes a front substrate and a rear substrate.
A sustain electrode, which includes alternately disposed X stripe electrodes and Y stripe electrodes, is formed on a lower surface of the front substrate and a bus electrode is electrically connected to the X and Y electrodes along the edges of the X and Y electrodes The X and Y electrodes and the bus electrode are covered by a front dielectric layer, and a protecting layer is coated on a surface of the front dielectric layer.
An address electrode crossing the sustain electrode is formed on an upper surface of the rear substrate and the address electrode is covered by a rear dielectric layer. A barrier rib that defines a discharge space is disposed on the rear dielectric layer. A phosphor layer of red, green, and blue colors is applied on an inner surface of the barrier rib and a surface of the rear dielectric layer.
The front substrate can be divided into a display area A that realizes images by forming pixels, and non-display areas B and C that are electrically connected to external terminals to transmit electric signals.
The bus electrode is formed on the sustain electrode that is formed on the front substrate. The bus electrode has a dual-layered structure including a first bus electrode coated on the surface of the sustain electrode and a second bus electrode coated on an upper surface of the first bus electrode.
The first bus electrode is a black layer functioning as a shielding layer, and the second bus electrode is a white conductive layer. In addition, the first and second bus electrodes have equal thicknesses on the display area A and the non-display areas B and C.
However, the bus electrode formed on the PDP has the following problems.
The bus electrode formed on the front substrate has the dual-layered structure including the black first bus electrode and the white second bus electrode on the display area and the non-display area.
When a raw material for forming the bus electrode is printed and developed, the first bus electrode is more vulnerable to a developing solution than the second bus electrode. Thus, undercut portions are generated on both edges of the bus electrode when it is formed.
Also, during an exposure process, since the first bus electrode receives less ultraviolet rays than the second bus electrode, the first bus electrode is less hardened than the second bus electrode. Thus, the first bus electrode has a larger undercut portion than the second bus electrode. If the undercut portion is large, it may cause a short.
In addition, due to the undercut portion, both edge portions of the bus electrode do not tend to contract downward. However, a center portion of the bus electrode tends to contract downward. Accordingly, the center portion of the bus electrode descends due to the contraction, and the edge portions rise, forming an edge curl portion on the bus electrode. When the edge curl portion is formed, a withstand voltage of the PDP is lowered.
In addition, since the thickness of the bus electrode patterned on the front substrate is constant on the display area and on the non-display area, the cost of fabricating the bus electrode on the non-display area that is electrically connected to the external terminal increase greatly when the size of the PDP becomes larger. On the non-display area, the black layer that is formed to improve the contrast on the display area is unnecessary.